Inteins are intervening proteins that catalyze their excision from flanking proteins, or exteins, via protein splicing. Inteins from archaeal extremophiles can be isolated as catalytically competent precursors and exhibit conditional protein splicing dependent on environmentally-relevant cues of temperature, pressure, salt concentration, and/or redox state. If an intein could serve a purpose for its host organism, it is likely that its splicing is conditional on such a cue. Using a combination of structural biology (NMR and fluorescence spectroscopy), in vitro enzymology, and genetic manipulation of intein-containing proteins, undergraduate research students will investigate the relationship between structure and function of temperature- and pressure-dependent inteins from deep sea thermophiles and of salt-dependent inteins from extreme halophiles, as well as characterize splicing in the native host. The long-term goal of the program is to understand how intein enzymes are able to catalyze chemical reactions and maintain structural stability under conditions that would irreversibly denature eukaryotic or prokaryotic proteins, and to determine if inteins can play a role for the host organism rather than being characterized as molecular parasites. Although inteins do not invade multi-cellular organisms, they interrupt key genes in some pathogenic bacteria, so understanding how splicing is regulated may provide insight into the role of these inteins. Inteins have found wide use in biotechnology applications, and a better understanding of their mechanism and structure may lead to the development of better tools for biomedical research.